Concussions are a type of traumatic brain injury (TBI) that is sometimes called a mild traumatic brain injury or a moderate traumatic brain injury and abbreviated as an MTBI. Concussions and the resultant chronic traumatic encephalopathy (CTE) have reached epidemic proportions in the US. The CDC estimates that as many as 3.8 million sports-related concussions occur in the U.S. each year including professional athletes, amateurs of all levels, and children. There are over 250,000 emergency room visits of young people annually for head injuries from sports and recreation activities. Over 50 million Americans participate in team sports and all of them are at some level of risk of experiencing a concussion. Concussions from multiple head blows and the resulting CTE have caused several professional football players to commit suicides. The US National Football League (NFL) and the scientific community recognize that concussions are a major concern for both players and the sport itself. Concussions also occur in college and high school football, in other sports such as ice hockey and cycling, and in military operations.
Concussions happen in the brain's white matter when forces transmitted from a big blow strain nerve cells and their connections, the axons, resulting in changes to the brain such as pruning, synaptic pruning, and myelination. Linear blunt trauma can happen when falling to the ground and hitting the back of the head. The falling motion propels the brain in a straight line downward. Rotational blunt trauma can occur when a player is spun, rolled or turned with the head hitting the object. The base of the skull is rough with many internal protuberances. These ridges can cause trauma to the temporal lobes during rapid deceleration. There is a predicted intracranial pressure wave after a concussive blow with the positive pressure (coup) to negative pressure (contre-coup) occurring across the brain. A high sheer stress occurs in the central core of the brain (e.g., brainstem). Axonal injury occurs with degeneration/disintegration in discrete regions of the brain. Axon retraction and areas of hemorrhage are noted.
Diffuse axonal injury (DAI) occurs from rotational forces. The injury to tissue is greatest in areas where the density difference is greatest. For this reason, almost ⅔ of DAI lesions occur at the gray-white matter junction. Location of injury depends on plane of rotation. The magnitude of injury depends on the distance from the center of rotation, arc of rotation, duration and intensity of the force. There are widespread metabolic changes (reduced N-Acetylaspartate (NAA)/Creatine (Cr), increased Choline (Cho)/Cr, and reduced NAA/Cho ratios). Early and late clinical symptoms, including impairments of memory and attention, headache, and alteration of mental status, are the result of neuronal dysfunction. The mechanical insult initiates a complex cascade of metabolic events. Starting from neurotoxicity, energetic metabolism disturbance caused by the initial mitochondrial dysfunction seems to be the main biochemical explanation for most post-concussive signs and symptoms. Furthermore, concussed cells enter a peculiar state of vulnerability, and if a second concussion is sustained while they are in this state, they may be irreversibly damaged by the occurrence of swelling. This condition of concussion-induced brain vulnerability is the basic pathophysiology of the second impact syndrome.
Prior Art Non-Ocular Concussion Assessment Methods and Systems
Current methods concussion assessment methods and systems are inadequate. The techniques used include: (a) questioning the athlete or person about the incident; (b) a sideline test with brief neurologic exam and follow up with a clinician; and (c) transferring the patient to medical facility to perform an emergency CT or MRI scan of the head.
Following a witnessed or reported traumatic force to the head, athletes are typically evaluated on the sideline or locker room with interrogation regarding relevant symptoms. More common symptoms include headache, dizziness, difficulty with concentration, confusion and visual disturbance or photosensitivity. Many also experience nausea, drowsiness, amnesia, irritability or feeling dazed. However, none of these symptoms either alone or in combination, are specific for concussion, and frequently concussions can be undetectable by symptom screening alone. Such a sideline evaluation is suboptimal. More specific testing is not readily available for most individuals and a delayed evaluation is the norm. For those seen later by clinicians, the neurologic exam is often normal. While CT scans are effective in detecting acute brain trauma such as hematoma or edema, they are limited in detecting concussions and other concussion-related symptoms because concussions affect brain function rather than structure. Thus, functional tools, such as functional MRIs (fMRIs) need to be used.
A fMRI is a concussion diagnostic tool used by medical professionals to measure the difference between the magnetic states of oxygen-rich and oxygen-poor blood through the use of blood-oxygen-level-dependent (BOLD) contrast techniques. These scans may not be readily available at most hospitals and the use is limited.
Further, specific clinical laboratory tests with professional specialists to interpret the data are not immediately available or even accessible to some players. There are presently some tests available for concussion assessment. Both balance and gait can also be affected in the setting of concussion, and numerous sideline assessments are intended to evaluate these sensorimotor functions.
The Standardized Assessment of Concussion (SAC) is a brief cognitive test that specifically evaluates orientation, concentration, and memory. While the test is easy to administer as a sideline screening tool, it suffers from inadequate sensitivity to justify its use as a stand-alone test. Furthermore, as with symptom checklists, determined athletes can manipulate the outcome, either by memorizing certain portions of the evaluation or by intentionally underperforming in the preseason baseline assessment to which subsequent tests will be compared. It lacks validity and reliability of the data obtained.
The Balance Error Scoring System (BESS) is a static balance assessment that requires an individual to perform 3 stances on 2 different surfaces for a total of 6 trials. Each trial is 20 seconds in duration, and the score is equal to the cumulative number of balance errors. While balance itself is a relatively objective measure of sensorimotor function, significant variability in scoring is reflected by poor interrater and even intrarater reliability. An individual's score on the BESS can also fluctuate during the course of an athletic season independent of concussion status, and the BESS score can be further confounded by lower-extremity injuries and/or fatigue.
The timed tandem gait test (TGT) is a dynamic assessment of sensorimotor function in which a participant is timed while walking heel-to-toe along a 38-mm-wide piece of tape that is 3 m in length. Each assessment consists of 4 identical trials, and the best time among the 4 trials is recorded as the official score. Timed TGT performance can be affected by exercise and lacks specificity for concussions and reliability.
The Sport Concussion Assessment Tool, 3rd Edition (SCAT-3) consists of a carefully selected series of tests, including a focused physical exam, a 22-symptom checklist, the GCS, and cognitive and sensorimotor assessments. The SCAT-3 benefits from its ability to assess a range of neurological functions, including orientation, cognition, memory, balance, and gait. However, the duration of the test battery is approximately 15-20 minutes, which is not optimal in the setting of time-limited athletic competition. Furthermore, the SCAT-3 is designed to be administered by medical practitioners, which limits its utility in youth and high-school sports, in which medical professionals are not necessarily available for sideline concussion screening. Similar to many of the other concussion screening tools, the SCAT-3 also requires baseline testing for comparison, which carries additional logistical challenges. Finally, SCAT-3 is not 100% sensitive for identifying athletes with concussion and is more of a complementary test rather than the primary stand-alone tool for concussion detection. The checklist's sensitivity has been shown to have a significant degree of variability. A revised SCAT-5 incorporates cognitive and balance testing with 6 pages of forms to complete and takes more than 10 minutes to complete. This test also cannot be used as stand-alone method to diagnose concussion.
The King-Devick Test (KDT) is a rapid mobile application of visual performance measure. It takes about two minutes to complete and compares pre-test results. This is a rapid number-naming task requiring the athlete to read aloud 3 cards of irregularly spaced single-digit numbers as quickly as possible. Scoring is based on both speed and accuracy. This test does not measure eye movements such as vergence or other oculomotor parameters, such as VOR or visual pursuit. This test also cannot measure fine ocular movements such as saccades. At its core, the KDT is an assessment of visual function, but it also assesses the integrity of attention. The KDT requires a baseline assessment for comparison. In the setting of sideline concussion screening, the KDT is ideal in that it takes less than 1-2 minutes to complete but is 80%-86% sensitive for detecting concussion and thus should not be used as a stand-alone test and has testing reliability variability due to large learning effect.
Brain Scope uses commercial smartphone hardware, using an Android operating system and a custom sensor to record and analyze a patient's electroencephalogram (EEG) after head, injury. The test is based on a technique called quantitative electroencephalography, or QEEG. QEEG relies on computerized analysis of a set of changes that are distinctive of a traumatic brain injury. It requires a baseline measurement because without a baseline measurement it can't be known for sure whether someone's EEG signal is in fact abnormal. The difference could be other things besides concussion, like a medication, a previous head injury, or something else entirely. It also requires trained personnel for interpretation and is not completely portable. It has not been well accepted, is more difficult to interpret and is more time consuming.
A blood test, called the Brain Trauma Indicator (BTI), helps determine whether a CT scan is needed in people with suspected concussion. The test measures two brain-specific proteins, ubiquitin C-terminal hydrolase (UCH-L1) and glial fibrillary acidic protein (GFAP), that are rapidly released by the brain into the blood within 12 hours of serious brain injury. Test results can be available within three to four hours (or approximately 16 hours after the serious injury). Low blood levels of these proteins indicate that, if the person has damage, it is likely too small to be seen on a CT scan. Obviously, this cannot be done acutely, but has to be done in a medical facility, which may not be readily available for remote injuries. Failure to provide information immediately, may also fail to prevent second events, as the athlete or military personnel may have returned to play or previous activities.
ImPACT (Immediate Post-Concussion Assessment and Cognitive Testing) is a neurocognitive assessment administered online in a controlled environment. ImPACT has two components: baseline testing and post-injury testing, which are used in conjunction to determine if a patient can safely return to an activity. ImPACT testing is a 25 to 30-minute online test. ImPACT is designed for ages 12-59. Only licensed healthcare providers can administer and interpret post-injury test and this is not available in most cities. It therefore cannot test the individual acutely and reliability is poor.
Helmet Instrumented Telemetry (HITS), that measures the magnitude and direction of an impact to a helmet is now used in some helmets, but do not appear to be reliable predictor of concussion or concussion severity.
Prior Art Ocular Concussion Assessment Methods
The ability to track objects in the environment is an important feature for humans to interact with their surroundings. In particular, the ability to recognize the presence of an environmental hazard is directly linked to our ability to fix our gaze on a visualized target of interest, recognize the threat, and implement a plan of action. Therefore, the central nervous system (CNS) is imposed with a series of tasks and time constraints that require a harmonic integration of several neural centers located in multiple regions and linked through an efficient transmission of information. There are central nervous system (CNS) impairments in individuals with mTBIs long after the last traumatic episode. Even a mild TBI (mTBI), also known as a concussion, will result in oculomotor abnormalities and can cause visual problems, including, but not limited to dysfunction with visual fixation on a visual element or visual object of interest and vergence. In addition to glare and photophobia, individuals commonly report problems including blurred vision; squinting; double vision/diplopia; difficulty reading; watching television; using computers; loss of visual acuity; color discrimination; brightness detection; contrast sensitivity; visual field defects; visuospatial attention deficits; slower response to visual cues; visual midline shift syndrome, affecting balance and posture; impaired accommodation and convergence; nystagmus; visual pursuit disorders; deficits in the saccadic system; extraocular motility problems resulting in strabismus; reduction in stereopsis; reading problems, including losing one's place, skipping lines, and slow reading speed.
During periods of fixation, our eyes are never perfectly stable but display small involuntary physiological eye movements. These take the form of disconjugate slow drifts (1-3′/˜0.05°), small conjugate microsaccades (5-10′/˜0.17°, 1-2 per second) and disconjugate tremors (15″/0.004°; 30-80 Hz) superimposed on the slow drifts. A further class of involuntary physiological eye movement is called saccadic intrusions (SI). They are conjugate, horizontal saccadic movements which tend to be 3-4 times larger than the physiological microsaccades and take the form of an initial fast eye movement away from the desired eye position, followed, after a variable duration, by either a return saccade or a drift Saccadic intrusions are involuntary, conjugate movements which take the form of an initial fast movement away from the desired eye position and followed after a short duration, by either a return secondary saccade or a drift.
When analyzing eye movement accuracy, abnormal saccadic eye movements while performing smooth pursuit, diminished accuracy of primary saccadic eye movement, and a widespread slower reaction to visual stimuli can all be seen. More commonly the most relevant saccadic parameters measured are peak velocity, latency, and accuracy. Visually guided saccadic tasks showed longer latencies and reduced accuracy irrespective of the severity of TBI. There is also increased eye position error, variability, widespread delays in reaction times and significant adaptations to normal patterns of eye tracking movements. Saccadic intrusions (irregular episodic occurrences of fast eye movements) are classified according to whether or not the intrusive saccades are separated by a brief interval in which the eyes are stationary. Although saccadic reaction times appear delayed in mild TBI, they can be seen to resume to normal levels one to three weeks after injury.
Saccadic intrusions, and saccadic oscillations are fixation instabilities which impair vision, and usually are involuntary and rhythmic. Saccadic oscillations are caused by abnormalities in the saccadic eye movement system. Abnormal saccades move the eyes away from the intended direction of gaze, and corrective saccades carry the eyes back. In saccadic intrusions, such as square-wave jerks and macrosquare-wave jerks, brief pauses occur, or intersaccadic intervals, between the opposing saccades. In ocular flutter and opsoclonus, no intersaccadic intervals occur. Three of four types of SI monophasic square wave intrusions (MSWI), biphasic square wave intrusions (BSWI) and double saccadic pulses (DSP) have been noted to be exclusively saccadic, while the fourth type, the single saccadic pulses (SSP), exhibits a slow secondary component. Following mTBI the impaired ability to generate predictive (or anticipatory saccades) can also be seen. The majority of individuals have vergence system abnormalities (convergence insufficiency), which typically results in oculomotor symptoms related to reading.
Thus, the measurement of ocular performance can greatly enhance the ability to determine whether a traumatic brain injury has occurred. However, the currently available ocular performance technology is not optimized for concussion evaluation.
The EYE-SYNC System quantifies the predictive timing of dynamic visuo-motor synchronization (DVS) between gaze and target during predictive circular visual tracking. Eye-Sync utilizes a head worn goggles which measures smooth pursuit, while the head remains motionless. The test takes 1 minute, while the user visualizes a dot moving in a circle. Eye trackers measures spatial and timing variability and has 80% test reliability for detecting concussions. However, visual pursuit testing cannot test the vestibular system, which is also intimately related to concussions. It therefore lacks more sophisticated testing, such as seen with vestibular ocular reflex testing. It is also not a stand-alone device, but requires an accessory computer attached.
The Eye-Guide Focus system features an eye-tracking headset and a portable chin mount. Its software runs on an iPad facing the user and the user has to follow a small white circle moving across the screen with their eyes in order to set the baseline of how their eyes normally function. This system lacks complete portability and uses similar technology to Eye-Sync.
Neuro Kinetics I-PAS System is a battery of tests using goggles and measures ocular motor, eye motor and reaction times to test whether certain neural pathways have been altered or are behaving abnormally. I-Pass test subjects wear a pair of goggles linked to a laptop and allows the tester to measure infinitesimally small changes in the subject's eye muscles while the test is taking place. The data generated from the test, coupled with the clinical exam, allows the doctor to make a final diagnosis. (a non-portable device). This testing is performed in a clinical environment, lacks portability and multiple pieces of equipment, with medical personnel required to interpret the data obtained.
Oculogica's EyeBOX uses ocular motility to detect cranial nerve function and provides a BOX Score indicative of the presence and severity of brain injury. The EyeBOX requires no pre-test calibration which can omit critical information if the subject being evaluated has indeed suffered a TBI or concussion. This test requires the user to rest their chin and forehead comfortably on the device and watch a video for less than four minutes. This requires laboratory testing and also lacks portability.
The evidence shows that more sophisticated testing is needed which is highly specific for concussion detection, portable and can be used on the field of play, in a military operative environment or in any other environment where a concussion is likely to occur. Specifically, oculomotor parameter measurement as described with this invention using ocular and head sensing elements and transducers have shown high sensitivity and accuracy in identifying athletes who experienced a sport-related concussion. When comparing all these tests, the VOR has the highest percentage for identifying the individual with concussions.
Background Regarding Concussion Mitigation
There are different types of forces, linear and rotational acceleration which act on the brain in any physical trauma. Linear accelerations are straight-line forces that begins at the point of impact. Rotational acceleration is less intuitive. It occurs most acutely during angular impacts, or those in which force is not directed at the brain's center of gravity. With violent blows to the head there is often a combination of linear and rotational forces. Most of the blows to the head will occur off-center and therefore most of the accelerations in the head are going to be rotational. These rotational forces strain nerve cells and axons more than linear forces resulting in greater neuronal injury.
Current methods for mitigating traumatic brain injuries are limited in their effectiveness. Although helmets typically provide decent protection against linear impacts, their protection against rotational impacts is deficient. This is clearly problematic given the severity of head injuries caused by rotational impacts. There is no pharmacologic treatment for any of these injuries. For these and other reasons, new technology and concepts must be implemented to improve helmet construction for impact protection, detecting and managing concussions and protecting the brain.
Studies of head impacts in football show that concussions occur when a person receives one or more hits that induce linear head accelerations of greater than about 80 g or rotational head accelerations of greater than about 5000 rad/see. An analysis of the speed at impact shows that a world-class sprinter can run about 10 m/sec (23 miles/hour). A 4-minute mile is equivalent to 6.7 m/sec, which is about ⅔ of the speed of a world-class sprinter. Football helmet test standards use 12 mile/hour impacts, which equals approximately 5 m/sec or half of the speed of a world-class sprinter. The padding on a typical football helmet is less than 1 inch thick. From physics:x=(0.5)a t2 v=a t (if acceleration is constant)
where: x is displacement, v=velocity, a=acceleration, and t=time
If one solves the above equations for constant deceleration from 5 m/sec to 0 m/sec in 1 inch ( 1/40th of a meter or 25 millimeters), the result is 500 m/sec2 or approximately 50 g (the acceleration of gravity is approximately 10 m/sec2). This means that padding that perfectly decelerates from 5 m/sec to 0 in 25 mm (1 inch) could theoretically provide a constant deceleration rate of 50 g. However, the padding on a helmet is far from this optimum in that (a) it doesn't provide a full inch of travel in actual use and (b) it doesn't provide the constant resistive force needed for perfect linear deceleration. Furthermore, athletes may sprint at speeds that create an impact having an initial velocity of greater than 12 miles per hour. A calculation of rotational accelerations based on typical current football helmet configurations shows that a one inch of rotation of the outer shell of a 12-inch helmet to stop an initial radial velocity of 12 miles/hour (5 m/sec) at a radius of 6 inches generates an angular acceleration of about 5000 rad/sec2 which is the concussion threshold as the threshold for linear acceleration (or deceleration) of the head. These theoretical calculations are consistent with the medical data that shows that concussions occur frequently in high school, collegiate, and professional football. Helmet manufacturers and the test labs understand the inability for current helmet designs to prevent concussions and place the following warning message on all football helmets sold in the USA: “No helmet can prevent all head and neck injuries a player might receive while participating in football”. Many warning labels on football helmets, such as those made by Riddell, go further in their warning label and also state that: “ . . . Contact in football may result in CONCUSSION-BRAIN INJURY which no helmet can prevent . . . .”